Do you remember grey goo? This was the plague of tiny machines that might one day devour the Earth and everything upon it. If the scientists got it wrong, nothing would remain but these man-made creatures, in their uncountable trillions.

We scoffed, but that was before we saw what Antony Gormley could do. This middle-aged Englishman has spent more than two decades replicating himself in stone, fibreglass and iron. Right now, forgetting about galleries and private collections, he has 131 life-sized copies in Merseyside and New York alone. The biggest and best known Gormley towers 20m over the A1 in Tyne and Wear.

The Angel of the North has no genitals, unlike many of Gormley's other sculptures, but its nickname is all too appropriate. Thanks to the "Gateshead Flasher" and its siblings, we are almost as familiar with Gormley's body as we are with our own. Some lonely art lovers have probably spent more time scrutinising his rough-cast bottoms than they have a living human's. In the world of sculpture, only Michelangelo's David and the Venus de Milo are more gawped at.

You can't entirely blame the artist for using himself as his model. His body, as he puts it, is "the closest experience of matter that I will ever have". But what will future generations make of this cult of the Gormley – assuming his rusty metal goo leaves room for future generations? Ours is a world with many competing notions of beauty, and Gormley does not claim to personify any of them. But will the humans of the 30th century realise that? Or will they snigger at his less-than-perfect body just as modern children giggle at David's dinky winky?

The question gets more urgent by the day. The plague has now reached Edinburgh, where six Gormleys stand in the Water of Leith. The artist has been making threatening noises about Glasgow and the Highlands. His works, he tells us, should last 1,000 years.